1. Field of the Invention
This invention relates to an imporvement of a device for controlling the position and direction of a bucket of a loader vehicle.
2. Description of the Prior Art
There is disclosed in the Japanese Utility Model Publication No. 30967/1974, a conventional means for automatically stopping in a desired position a bucket adapted to be actuated to tilt and dump by the action of a bucket tilting cylinder. The conventional means comprises, as shown in FIG. 1, a bucket cylinder "a" provided with a piston rod "b", the leading end "c" of which may extend between extreme positions "A" and "B" through an intermediate detecting position "C" by dump operation. When the leading end "c" of the piston rod is located between the most outwardly extended position "A" and the intermediate position "C", an electromagnet for holding a change-over valve is energized. If the changeover valve is moved to a tilt-back position in this condition, the position of the change-over valve is temporarily restrained by the action of a magnetic force so that the bucket may effect tilt-back operation continuously. When the tilt-back operation has been made to achieve a posture of the bucket so that the leading end " C" of the piston rod "b" moves beyond the position "c", an operative member "d" adapted to move together with the piston rod "b" will be brought into contact with an electric switch "e" so that the latter may be deenergized and the bucket may move back to its neutral position by its self-returning action, thereby enabling the bucket to stop at that position and assume a predetermined posture.
In the above-mentioned conventional means, as described hereinabove, when the bucket occupies its dumping position and the leading end "c" of the piston rod "b" is located between the positions "A" and "C", the electromagnet is energized so as to restrain the change-over valve in position by the magnetic force thereof. Therefore, there has been a problem in which upon manipulation of the change-over valve to repeatedly effect tilting and dumping operations of the bucket under such a condition, a large manual operating force is required for the operator to overcome the magnetic force, and so not only it casts a burden for him, but also it becomes impossible for him to effect the change-over operation.
According to the conventional means, there has been another problem in which when the leading end "c" of the piston rod is retracted to any desired position between the positions "C" and "B" and stopped at that position, it is absolutely necessary to artificially hold the change-over valve so as not to allow it to return to its neutral position by its self-returning action, and such artificial holding of the change-over valve is liable to confuse the operator in operation. U.S. Pat. No. 3,823,647 discloses another type of electromagnetic bucket positioner for loader vehicles. In this device too, however, the operator is required to move the control valve from the rack-back position against the magnetic force of the electromagnet means.